inet: Add getsockopt support for IP_ROUTER_ALERT and IPV6_ROUTER_ALERT

Currently getsockopt does not support IP_ROUTER_ALERT and
IPV6_ROUTER_ALERT, and we are unable to get the values of these two
socket options through getsockopt.

This patch adds getsockopt support for IP_ROUTER_ALERT and
IPV6_ROUTER_ALERT.

Signed-off-by: Juntong Deng <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/inet_sock.h

···
 	INET_FLAGS_REPFLOW	= 27,
 	INET_FLAGS_RTALERT_ISOLATE = 28,
 	INET_FLAGS_SNDFLOW	= 29,
+	INET_FLAGS_RTALERT	= 30,
 };
 
 /* cmsg flags for inet */

net/ipv4/ip_sockglue.c

···
 {
 	struct inet_sock *inet = inet_sk(sk);
 	struct net *net = sock_net(sk);
-	int val = 0, err;
+	int val = 0, err, retv;
 	bool needs_rtnl = setsockopt_needs_rtnl(optname);
 
 	switch (optname) {
···
 
 	/* If optlen==0, it is equivalent to val == 0 */
 
-	if (optname == IP_ROUTER_ALERT)
-		return ip_ra_control(sk, val ? 1 : 0, NULL);
+	if (optname == IP_ROUTER_ALERT) {
+		retv = ip_ra_control(sk, val ? 1 : 0, NULL);
+		if (retv == 0)
+			inet_assign_bit(RTALERT, sk, val);
+		return retv;
+	}
 	if (ip_mroute_opt(optname))
 		return ip_mroute_setsockopt(sk, optname, optval, optlen);
 
···
 		goto copyval;
 	case IP_BIND_ADDRESS_NO_PORT:
 		val = inet_test_bit(BIND_ADDRESS_NO_PORT, sk);
+		goto copyval;
+	case IP_ROUTER_ALERT:
+		val = inet_test_bit(RTALERT, sk);
 		goto copyval;
 	case IP_TTL:
 		val = READ_ONCE(inet->uc_ttl);

net/ipv6/ipv6_sockglue.c

···
 		if (optlen < sizeof(int))
 			goto e_inval;
 		retv = ip6_ra_control(sk, val);
+		if (retv == 0)
+			inet6_assign_bit(RTALERT, sk, valbool);
 		break;
 	case IPV6_FLOWLABEL_MGR:
 		retv = ipv6_flowlabel_opt(sk, optval, optlen);
···
 
 	case IPV6_RECVFRAGSIZE:
 		val = np->rxopt.bits.recvfragsize;
+		break;
+
+	case IPV6_ROUTER_ALERT:
+		val = inet6_test_bit(RTALERT, sk);
 		break;
 
 	case IPV6_ROUTER_ALERT_ISOLATE: